Homopolymers have properties which are characteristic for each type of polymer.
Low density polyethylene generally has good film forming properties and is generally competitive with other polymeric materials in this application, but it does not have high transparency or clarity in molded applications. By contrast, polystyrene does not have good film forming properties, but it does have good transparency and clarity in molded applications.
There are numerous other illustrations of distinctive sets of physical, electrical, chemical and mechanical properties which are manifested by types of polymers including polyvinyl chloride, polyacetal, polyamides, polyethers, polyolefins, etc., and which are manifested by different species of a polymer type as, for example, nylon 6, nylon 11, nylon 66, etc.
It is sometimes possible to combine properties of different types of polymers or species members by forming blends. Blends may be formed where it is found that the polymers are naturally compatible, i.e., where it is found that one polymer can be mixed with or dissolved in another polymer without the involvement of permanent chemical reaction, but with a resultant intimate uniform intermixing of the two polymers to give an apparent homogeneous composition which does not separate into its ingredient components or segregate during ordinary processing such as heating and conventional forming as by extrusion, molding, etc., and which does not segregate after processing with ordinary use or aging. Naturally occurring blends may exhibit combinations of properties which are greater than the average of the blend ingredients for the proportions of the ingredients in the blends.
The compatibility of different polymers occurs naturally for certain polymers and species members. For example, polyphenylene oxide polymer is naturally compatible with polystyrene, both of which are glassy-type polymers. The polyphenylene oxide and polystyrene are the principal ingredients of the family of polymeric materials in different proportions which are available from the assignee of this application under the trade designation NORYL.RTM..
By naturally compatible is meant that the compatibility is evident and persistant from blending which occurs readily with conventional heating and mixing and without any modification of the ingredients of the blend and without any specific blending agents, although conventional additives such as antioxidants, coloring agents, etc. may be included.
Naturally occurring polymer blends, such as those of the NORYL family of polymers, may exhibit a single apparent thermodynamic response when subjected to calorimetric measurements in which specific heat is measured as a function of increasing or decreasing temperature. Where such a single apparent thermodynamic response is found for a blend of polymers, it indicates that the constituents are alloyed or dissolved in each other. The apparent thermodynamic response of a true alloy is generally proportional to the proportions of the constituents of the alloy.
Such exhibition of a single apparent thermodynamic response is the exception inasmuch as the polyphenylene oxide and the polystyrene constituents of these compositions are true blends in that the constituents are present as true solutions or alloys and the formation of true solutions of distinct types of polymers is rare and unique. For such a true solution or alloy, the apparent thermodynamic response is also distinct from that exhibited by a mixture of two types of polymers which are not naturally compatible and which do not form true solutions or alloys.
Mixtures of polymers into pseudo alloys or pseudo solutions can be detected by calorimetric measurements and are found to exhibit the separate changes in the specific heat curve which is representative of the separate and unalloyed ingredients which are present.
As used herein, the term alloy blends or solution blends is meant to indicate the types of blends which exhibit the unique set of apparent thermodynamic behaviors as discussed immediately above with reference to the NORYL.RTM. family of natural blends.
By contrast, the term polymer blends or blends is meant to refer to compositions which, even when in very intimate state of intermixing at or near a molecular level, are not known to exhibit such distinct and unique apparent thermodynamic behavior as that exhibited by alloy blends or true blends such as NORYL.RTM.. However, the term blends as used for combined or mixed polymers is not intended to mean that a molecular level of intermixing is achieved or even achievable for a combination of polymers which are mixed. The degree of mixing which is achieved for a given level of mixing effort or energy expended is largely dependent on the affinity of one polymer of a mixture for the other polymer or polymers of the mixture. For most polymer combinations, the affinity or compatibility factor prevents a very intimate or molecular level of mixing to be achieved with the level of mixing attainable by conventional industrial polymer procesing and mixing equipment.
Generally, such blends or mixtures of different types of polymers are not readily formed and the properties of such blend compositions as can be formed have not brought such compositions into prevalent use in the plastic industry. A higher level of blending does occur among different types of rubbers and some blends are formed and used commercially in the rubber industry.
Generally also, the blends of different types of polymers with rubbers are not readily formed to produce products having commercial utility.
As used herein, the term polymer or resin is intended to include both naturally occurring and synthetic polymers and, accordingly, to include natural and synthetic rubbers, and polymers such as polyolefins, polyamids and other synthetic resins.
Also in general, the affinity of one polymer type for another type in the sense of the degree of blending or dispersing which can be attained will depend on numerous compatibility or incompatibility factors, such as chemical formula, chemical architecture, molecular weight, polarity, degree of crystallinity, rheological properties, first and second order thermodynamic responses, including melting point and glass transition temperature, as well as on other factors.
An important element in the properties which are exhibited by a blend of polymer materials is the degree of intermixing which is achievable and achieved and the intimacy of the contact of one polymer material with another in a mixture or blend. This degree of intermixing depends as indicated above on the affinity of two polymer materials for each other based on numerous factors discussed above and also on the energy expended in causing the intermixing. Intermixing factors include the temperature of processing, the level of shear developed, the pressure on the system, the time of processing and several other factors. It also depends on the presence of mixing or blending aids.
The term dispersion as found in technical materials dictionaries refers to material systems having two materials present in different phases, one of which, as for example liquid, is continuous and the other of which, as for example gas or solid, is discontinuous. However, according to Webster, the term disperse means "to break up and scatter in all directions; spread about; distribute widely", along with alternative definitions. Webster defines a dispersion as "a dispersing or being dispersed" also along with alternative definitions.
As used herein, the term interdisperse and its derivatives such as interdispersion, means the action of breaking up and scattering of at least one polymer material into at least another and distinct polymer material, while at least one of the polymer materials is undergoing flow, which results in internal shear. The term interdispersion also means the product of the action. At least two distinct polymer materials are involved in formation of an interdispersion and the composition contains also the dispersed fibrous interdispersing agent of this invention.
Surprisingly, it has now been found that certain agents are uniquely adapted to enhance the dispersing of a first polymer into a second polymer to form a multipolymer interdispersion of any desired degree of intimacy of contact of the first and second polymers.
The formation of interpolymer interdispersions pursuant to this invention has been demonstrated to be feasible for polymers which have very little or no affinity for each other.
Polymer affinity factors may be classified according to a number of different groupings. For example, some polymers such as polyethylenes are more highly crystalline and are in a class of more highly crystalline polymers generally having a sharper softening or melting point. Low density polyethylene is about 55 to 60% crystalline and high density polyethylene is over 90% crystalline. Others are classified as glassy polymers and these soften over a wider temperature range. There are essentially no naturally compatible or easily formed binary blends of highly crystalline polymers such as polyethylene with the more glassy polymers such as polyvinyl chloride.
However, more highly crystalline polymers can be interdispersed with the more glassy polymers using the interdispersing agent of this invention. For example, low density polyethylene has been interdispersed pursuant to this invention with polyvinyl chloride, although it is widely recognized in the art that low density polyethylene and polyvinyl chloride are extremely incompatible. By itself, this demonstrated interdispersability of low density polyethylene directly with polyvinyl chloride with the aid only of an interdispersion agent is deemed to demonstrate an extraordinary and remarkable interdispersing capability of the agent. The product formed is an interdispersion of each polymer in the other and the degree of dispersion achievable can make the composition comparable to a blend.
Other polymers are classified in a group of more amorphous materials or rubbery polymers. Generally, members of the amorphous group such as ethylene propylene rubber are not naturally compatible with either the more glassy polymers such as polyvinyl chloride nor with the more highly crystalline polymers such as polyethylene.
An important attribute of the agent is that it permits interdispersing of distinctly different polymers to any desired degree, but at the same time, interlocks the interdispersed polymers as explained more fully below so that they resist separation even though the degree of interdispersion is less than at the molecular level and, in fact, low on a relative basis, i.e., relative to the tendency of the components of a mixture to separate responsive to separating influence such as selective solvent action.
However, with the aid of the interdispersing agent of this invention, interdispersions of highly crystalline polymers may be formed with the more glassy polymers. For example, ethylene propylene rubber polymer can be and has been blended with high density polyethylene.
Also, the highly crystalline polymers can be blended with the more glassy polymers as, for example, polystyrene, which is a largely glassy polymer, has been interlocked as a blend with Delrin, which is polyacetal and is a highly crystalline polymer.
Also, some polymers are classified as more highly polar and other polymers are classified as non-polar. Generally, more highly polar polymers do not blend readily and naturally with non-polar polymers. However, more highly polar polymers such as polyvinyl chloride may be interdispersed with non-polar polymers such as high or low density polyethylene.
By naturally occurring blends as used herein is meant blends which are formed readily with ordinary and conventional heating and mixing and which persist due to the inherent compatibilities of the components of the blend. Such compatibility may be due to similar molecular and chemical structure. For example, chlorinated polyethylene blends to a degree with natural rubber or with styrene butadiene rubber as pointed out in U.S. Pat. No. 4,262,098.
However, some polymers which may appear to have similar molecular and chemical structure do not blend naturally, i.e., readily with ordinary heating and mixing and without the aid of blending agents. For example, high density polyethylene does not blend readily and easily with low density polyethylene by ordinary and conventional heating and mixing. Nevertheless, high density polyethylene is interdispersable with low density polyethylene at low levels of energy input to form interdispersions with the aid of the interdispersing agent as provided pursuant to the present invention.
It will be understood that the formation of certain blends may be brought about by application of higher energy processing conditions than are ordinarily used and ordinarily preferred in forming polymer compositions.
For example, if high temperature are employed in an effort to blend high density polyethylene with low density polyethylene, it is probably feasible to find a set of blending conditions at which an apparent blend will form. The set of conditions can involve high temperature, high pressure, high level of mechanical energy input or agitation and other high energy inputs.
However, as a general rule, a polymer material has a useful life expectancy which is related to the thermal and other energy history which it has experienced in the processing and fabrication stage. Accordingly, it is desirable generally to process a polymer and fabricate an article from a polymer at a lower set of energy input conditions and particularly at lower temperatures and lower time at temperature in order to preserve as much as possible of the inherent useful life expectancy of the polymer.
To avoid the harsh processing conditions which may be needed to form apparent blends and to gain the advantage of sets of properties which are not available in homopolymers, copolymers have been formed by chemical techniques. Accordingly, to overcome the incompatibility of different polymers, and in order to make compositions available which have combinations of properties which are not found in any of the individual polymers, chemical combinations of different monomers are made under suitable polymerization conditions to form copolymers.
For example, ethylene monomer, principally used in making polyethylene, and propylene monomer, principally used in making polypropylene, can be copolymerized under suitable conditions to make ethylene-propylene copolymer or ethylene-propylene rubber.
Similarly, the monomers used in making polyacrylonitrile, polybutadiene and polystyrene as distinctive individual polymers can be copolymerized to form ABS copolymer, or acrylonitrile-butadiene-styrene copolymer.
Generally, a different set of polymer properties are obtained in the copolymers formed by copolymerization of the distinct monomers in combination than are obtained by separately polymerizing the individual monomers to their respective homopolymers. For example, while neither polyethylene nor higher molecular weight polypropylene has distinctly rubbery properties, some ethylene propylene copolymers have distinctly rubbery properties.
The cost of copolymers is generally substantially higher than the cost of the homopolymers made from the individual monomers.
Polypropylene and low density polyethylene are at best poorly compatible polymer species in that only small percentages, if any, of either one can be blended into the other through conventional blending methods and means. At higher concentrations, the species are incompatible and do not form homogeneous blends.
Surprisingly, it has now been found that using conventional mixing and blending practice and equipment, interdispersions of normally incompatible ratios of polyethylene and polypropylene, is made feasible by the use of a small amount of an interdispersing agent pursuant to this invention.
The number of copolymers which can be formed by copolymerization reactions is limited. This is partly because the polymerization conditions, the polymerization catalysts, and the polymerization mechanism differs for many polymer species. For example, not all monomers, such as olefin monomers which can be polymerized by one of the "addition" type mechanisms, can be copolymerized with monomers, such as esters, which are polymerized by "condensation" type mechanisms. Accordingly, it is not feasible to form copolymers by copolymerizing all combinations of selected monomers.
Different polymer species, the distinct monomers of which could not be formed into copolymers by presently existing technology, can nevertheless be interdispersed in each other with the aid of the interdispersing agents of this invention to achieve combinations of properties which have not heretofore been available.
Copolymers are prepared commercially in certain preferred monomer ratios to give the copolymer formed preferred combinations of properties. For example, ethylene vinyl acetate copolymer prepared from the ethylene monomer and the vinyl acetate monomer will have a more rubbery set of properties if the ratio of ethylene monomer to vinyl acetate monomer is at one value, for example, 25% of vinyl acetate, and will have a less rubbery set of properties if the ratio of monomers is at another value, for example, 3% vinyl acetate.
However, it is not commercially feasible to alter the ratio of monomers for each specific end use application to which the copolymer may be put. Rather, the commercial product is produced with a certain number of monomer ratios, and the end user must try to adapt the commercially available materials to the end use contemplated. Further, for those set numbers of copolymers which are produced, the supplier and wholesaler must stock all or most of them to satisfy his customer's needs.
However, it is feasible to modify the properties of interdispersions of otherwise poorly compatible or incompatible homopolymers by interdispersing two incompatible polymers with the aid of an interdispersing agent of this invention in any desired or selected ratio of homopolymers, and to achieve the properties which are the result of such interdispersing in any such selected ratio.
Moreover, such dispersing can be achieved without the aid of chemical polymerization equipment and can be accomplished for most binary polymer systems through use of existing and commercially available mixing and processing equipment such as rubber mills, plastic mills, extruders, high intensity mixers and the like.
Accordingly, this invention makes possible the custom interdispersing by the end user of different combinations of polymers to achieve a desired set of properties for particular end uses to a degree not previously possible.
Further, the invention is not confined to the interdispersing of binary sets or combinations of homopolymers, but extends to the interdispersing of tertiary combinations of homopolymers, quaternary combinations of homopolymers, and other multinary combinations of homopolymers in all ratios and proportions. Multinary as used herein means sets of two or more members in combination without limitation as to any upper number of members and includes sets of five or six or more homopolymer members.
In addition, interdispersions of combinations of homopolymers with incompatible or poorly compatible copolymers can be made in binary sets and/or multinary sets without limitations as to the number of members in a set nor as to proportions nor as to the number of homopolymers as contrasted with copolymers in the set. On the same basis, multinary sets of copolymers can be combined and interdispersed in all ratios and proportions.
Another form of copolymer which is even more difficult to produce than the ordinary random copolymer and which is also used in efforts to blend polymers is the block copolymer form. This form has a set of a first monomer species such as "A" polymerized in a first block "AAAAAA" and another set of a second monomer species "B" polymerized in a second block "BBBBBB". Repeating alternate blocks gives the polymer a form which may be represented as follows: EQU AAAAA BBBBB AAAAA BBBBB AAAAAA
One set of such polymers which has been used widely is the set which has alternating blocks of polystyrene and polybutadiene and which are sold commercially by the Shell Oil Company under the designation Kraton.
The Kratons are thermoplastic rubbers and have a combination of thermoplastic properties, due to the presence of the blocks of polystyrene, and rubber properties, due to the presence of blocks of the polybutadiene.
However, pursuant to the present invention, interdispersions of different polymers, such as polystyrene and polybutadiene, can be formed to yield interdispersed compositions having unique sets of properties.
The properties of polymer species occur in sets in the sense that one polymer species has a certain specific density, softening temperature, izod impact, tensile strength and other physical, chemical, electrical, mechanical and thermal properties, all of which are subject to measurement and which can accordingly be quantified. The sets of properties of the different polymers and different members of families of polymers such as the polyolefins have been measured and are known.
It is the current practice in the plastics industry that when a choice is made of a polymer for a particular end use, it is made on the basis of the material and processing cost and on the basis of the appropriateness of a particular set of properties for the intended end use.
When an interdispersion of polymers is made pursuant to the present invention, although the starting sets of properties of each individual ingredient polymer is known, not all of the combination or set of properties which will result from the interdispersing is readily apparent or highly predictable. For example, as is pointed out below in Example 1, a material which is known to have high flexibility, such as a rubber, may be chosen as one constituent of an interdispersion to lend flexibility to the interdispersion. Where increased toughness is sought, a second although normally incompatible constituent may be selected to impart toughness or abrasion resistance to the interdispersion. However, although it is expected that an interdispersion can be formed pursuant to the present invention having some combination of flexibility and toughness properties, there is no way of predicting quantitatively just what properties will result from the intimate interdispersion with the interdispersing agent of this invention of materials which are otherwise incompatible or poorly compatible under a given or a particular set of conditions used in forming a particular interdispersion.
In Example 1, the properties found and reported are not the properties only of the interdispersion of high density polyethylene with ethylene propylene rubber. In fact, almost no properties of this composition were measured although several were observed, i.e., the material handled well and processed well and extruded well as contrasted with the inferior observed properties of the material of Example 2 which did not contain the dispersing agent of this invention, which did not handle well or process well or extrude well.
Considering now the interdispersing agents of this invention, it has now been discovered that very long chain polymers of polytetrafluoroethylene and of polyethylene of very high and ultra high molecular weight exhibit a unique and unexpected behavior in inducing the interdispersion of a first polymer into a second and distinct polymer as the polymers are subjected to a motion which induces shear within the polymers.
The term interdispersion as used herein is meant to include the dispersion of a first polymer into a second polymer as well as the dispersion of the second polymer into the first either simutaneously or sequentially and to include an interdispersion of both polymers into each other simultaneously. For purposes of this invention, either the first and/or second polymer may be a homopolymer, copolymer, or combination of polymers, either naturally occuring blends or combinations of poorly compatible or incompatible polymers induced into interdispersions by the interdispersing agents of this invention.
These interdispersing agents have been found to be effective in combining distinct polymers into interdispersions with a generally lower level of energy input than is needed to form blends which have an equivalent degree of intimacy of contact of the constituents as can be formed in the absence of the interdispersing agents of this invention.
For example, as is pointed out in Example 31 below, it has been found that an apparent blend of polyethylene and polystyrene can be formed on a mill at a temperature of 310.degree. F. However, at 240.degree. F., the same ingredients do not enter an apparent blend to any observable extent. However, at 240.degree. F., the polyethylene and polystyrene can be interdispersed to form a composition which has an appearance on the mill closely resembling the apparent blend formed at the higher temperature of 310.degree. F. The interdispersing agents can also form interdispersions of combinations of polymers which do not form apparent blends at higher energy levels as, for example, at higher temperatures or other higher energy input levels.
As understood by the applicants, the unique ability of the interdispersing agents to form interdispersions of incompatible polymers and to form interdispersions of poorly compatible polymers at lower energy levels is related to the ability of these agents to extend into fibrous form and to disperse through the polymer in this fibrous form as the host polymers undergo internal shearing action by the working or processing of the polymers.
The applicants herein are not the first ones to discover the unique morphology of the polytetrafluoroethylene which has now been discovered by the applicants to be an intrdispersing agent. Nor are they the first ones to discover the influence on a single polymer of fibrous polytetrafluoroethylene.
U.S. Pat. No. 3,132,116 issued in the name of one of the inventors of this application and assigned to the assignee of the subject application, discloses that if a silicone polymer is blended with filler and other conventional ingredients in the presence of a minor amount of tetrafluoroethylene polymer, the characteristic tackiness of the blended mixture is dramatically reduced, and, in addition, that the properties of elastomers derived therefrom are improved, compared to elastomers derived from such mixtures free of polytetrafluoroethylene.
By contrast to the subject matter of the U.S. Pat. No. 3,132,116 which deals only with a treatment of a single polymer, i.e., treatment of silicone polymer with PTFE, the compositions of the present invention comprise at least two polymers of distinct properties to which polytetrafluoroethylene is added, and the interdispersions of these distinct polymers into each other with the aid of the PTFE.
In addition, the PTFE addition has been found to make important changes in the properties of the combined polymers of this invention to which it is added as, for example, the rate at which the interdispersed polymers can be dissolved in comparison to the rate at which a blend or mixture of the same polymers can be dissolved in the absence of PTFE.
A significant advantage of the present invention is that it makes possible for the first time for many binary and other multinary systems of polymers a very effective and efficient means and method for bringing together in very intimate intermixed contact or intimate interdispersions polymers which cannot otherwise be so easily intimately blended and intermixed. To achieve an equivalent degree of intimacy of intermixing would otherwise require expensive or cumbersome or extraordinary means and measures, and as is pointed out above, such extraordinary measures can detract from the combined properties of the polymers which are combined.
It should be pointed out that because of the fibromorphous character of the dispersing agent of this invention, the dispersions which are formed have coherency and integrity of structure even though the extent of interdispersion is brought to an optimum degree.
Generally, an optimum degree of dispersion can be achieved in a relatively short processing time, which may be of the order of minutes or hours, depending on the degree of internal shear induced in the polymers. For the processing of a relatively small quantity of a combination of polymers as, for example, low density polyethylene and PVC on a small plastic mill, each of which polymers is millable at the time of processing, an effective interdispersion can be achieved in a period of about 10 minutes and a higher degree of interdispersion can be achieved in 20 or 30 minutes where the degree of interdispersion is measured by rate of burning of a horizontal strip of the product interdisperion. Clearly, however, the degree of interdispersion can be controlled as, for example, by controlling the time and temperature of milling and intensity of agitation.
An optimum degree of interdispersion is deemed to result in an intimate contact of the different polymers at a level approaching a molecular level although the applicants have no direct evidence of such molecular level of contact and do not wish to be bound by the accuracy of this prognosis.
But the inventors have found that for numerous compositions which have been formed on a mill, for example, without the dispersing agents of this invention, the milled mixture does have less coherency and integrity when processed under a given set of conditions for a given time and temperature as compared to the coherency and integrity of a composition of the same ingredients processed under the same set of conditions for the same time with the aid of an interdispersing agent of this invention.
This rapid development of integrity of a composition of two normally incompatible polymers is dramatically demonstrated when quantities of the two polymers are placed on a mill and subjected to milling action for a given period of time. As illustrated by the examples below, where the two polymers are milled for a given time and temperature, frequently there is no evidence of interdispersing of blending or intimate mixing of the two polymers.
If a first half of the milled composition is then removed from the mill and the dispersing agent of this invention is added to the second half of the composition remaining on the mill, a very rapid and dramatic interdispersing of one polymer into the other will be observed in the second half of the composition.
If this second half polymer dispersion is then removed from the mill and the first half of the composition, free of the dispersing agent, is returned to the mill, it will be observed that the milling can be continued for a significant time beyond that which resulted in formation of the interpolymer dispersion of the second half composition containing the dispersing agent.